REALPATH(3)

NAME
realpath - return the canonicalized absolute pathname

SYNOPSIS
#include <limits.h>
#include <stdlib.h>

char *realpath(const char *path, char *resolved_path);

DESCRIPTION
realpath expands all symbolic links and resolves references to '/./', '/../' and extra '/' characters in the null terminated string named by path and stores the canonicalized absolute pathname in the buffer of size PATH_MAX named by resolved_path. The resulting path will have no symbolic link, '/./' or '/../' components.

RETURN VALUE
If there is no error, it returns a pointer to the resolved_path. Otherwise it returns a NULL pointer, and the contents of the array resolved_path are undefined. The global variable errno is set to indicate the error.

ERRORS

EACCES
    Read or search permission was denied for a component of the path prefix.

EINVAL
    Either path or resolved_path is NULL. (In libc5 this would just cause a segfault.)

EIO An I/O error occurred while reading from the file system.

ELOOP
    Too many symbolic links were encountered in translating the pathname.

ENAMETOOLONG
    A component of a path name exceeded NAME_MAX characters, or an entire path name exceeded PATH_MAX characters.

ENOENT
    The named file does not exist.

ENOTDIR
    A component of the path prefix is not a directory.

BUGS
The libc4 and libc5 implementation contains a buffer overflow (fixed in libc-5.4.13). Thus, suid programs like mount need a private version.

The length of the output buffer should have been an additional parameter, especially since pathconf(3) warns that the result of pathconf() may be huge and unsuitable for mallocing memory.

HISTORY
The realpath function first appeared in BSD 4.4, contributed by Jan-Simon Pendry. In Linux this function appears in libc 4.5.21.

CONFORMING TO
In BSD 4.4 and Solaris the limit on the pathname length is MAXPATHLEN (found in <sys/param.h>). The SUSv2 prescribes PATH_MAX and NAME_MAX, as found in <limits.h> or provided by the pathconf() function. A typical source fragment would be

    #ifdef PATH_MAX
      path_max = PATH_MAX;
    #else
      path_max = pathconf (path, _PC_PATH_MAX);
      if (path_max <= 0)
        path_max = 4096;
    #endif

The BSD 4.4, Linux and SUSv2 versions always return an absolute path name. Solaris may return a relative path name when the path argument is relative. The prototype of realpath is given in <unistd.h> in libc4 and libc5, but in <stdlib.h> everywhere else.

SEE ALSO
readlink(2), getcwd(3), pathconf(3), sysconf(3)